Effect of Differences in the Orientation of Adsorbed Molecules and in the Magnitudes of Limiting Capacitances of the Inner Part on the Regularities of Coadsorption of Two Organic Substances

The Alekseev–Popov–Kolotyrkin model, complemented with a set of mixed Frumkin isotherms, is used to perform an analysis of joint adsorption of two neutral organic substances when there are substantial differences in (1) limiting potential drops ψN1 and ψN2 and (2) capacitances of the inner part at θ1 = 1 and θ2 = 1. It is shown that in the absence of a lateral interaction between coadsorbed species and at a certain ratio between their concentrations, in either case there exists a region of potentials where the set of isotherms has three solutions. The stability of these solutions is characterized and the curves of the differential capacitance (equilibrium and nonequilibrium) and the interfacial tension are calculated. A general analysis of the set of isotherms in the region of physically reasonable values of adsorption parameters is conducted.